Vol. 124 (2013) ACTA PHYSICA POLONICA A No. 2

Special Anniversary Issue: Professor Jan Czochralski Year 2013 � Invited Paper

Development of Growth Technologies for the Photonic Single

Crystals by the Czochralski Method at Institute

for Single Crystals, NAS of Ukraine

M.B. Kosmyna, B.P. Nazarenko, V.M. Puzikov and A.N. Shekhovtsov∗

Institute for Single Crystals, NAS of Ukraine, Lenin Ave. 60, 61001, Kharkov, Ukraine

The present paper brie�y overviews the application of the Czochralski method for growth of a set of oxidecrystals for photonics, as well as the design of equipment at the Institute for Single Crystals, NAS of Ukraine.The examples of crystal growth and their characterization are described. The simultaneous Q-switched lasing andself-Raman frequency conversion were demonstrated in Nd-doped PbWO4 and PbMoO4 crystals grown by theCzochralski method. The slope lasing e�ciency obtained for a PbMoO4:Nd

3+ laser is the best result for all thecrystals with the scheelite-type structure. A detection unit with high scintillation characteristics based on a largevolume (V ≈ 350 cm3) CdWO4 crystal was produced. Crystal growth procedures and properties of new doubletungstate and vanadate crystals are presented, too.

DOI: 10.12693/APhysPolA.124.305

PACS: 81.10.Fq, 42.70.Hj, 42.70.Mp, 29.40.Mc

1. Introduction

The use of the Czochralski method at Institute for Sin-gle Crystals NAS of Ukraine (the Institute) was moti-vated by a need to produce laser elements for new facil-ities. Investigations in the �eld of lasers were started atthe Institute as long ago as in 1961. This was a turning--point in the development of physics and optics and thechange-over to optical quantum generators (OQG). In-tensive investigations in the �eld of quantum electron-ics were carried out under the leadership of Nobel Priz-ers Prokhorov and Basov at Institute of General Physics(Moscow, Russia), USSR Academy of Sciences, and atother laser centres of the world. In Ukraine these investi-gations were started at Institute for Single Crystals andInstitute of Physics (Kiev, Ukraine), NAS of Ukraine.At that time, one of the main active elements for OQGs

was neodymium-doped calcium tungstate single crystal(CaWO4:Nd3+). The �rst continuous-wave laser operat-ing at room temperature was designed on the base of thiscrystal at Institute of General Physics, USSR Academyof Sciences (Moscow, Russia).The Czochralski method was the main stage of produc-

tion technology of high-temperature oxide single crystals.Its potentialities were realized due to modernization ofthe available setups for thermal treatment of metallic ma-chine parts. These setups were transformed into growthapparatuses and then used for the growth of Y3Al5O12

yttrium�aluminium garnet (YAG) and calcium tungstatesingle crystals.The design of new facilities of �OKB-63� type ac-

cording to the speci�cations of the Institute essentially

∗corresponding author; e-mail: shekhov@isc.kharkov.ua

speeded up the technological work on the growth of high--temperature single crystals. However, the most impor-tant breakthrough in the development of laser garnetcrystals was made in 1972 when new-generation setups�Donets-1� (made by the design department �Donets�,Ukraine) were put into operation.Since 1972, laser elements based on YAG crystals have

practically completely ousted calcium tungstate elementsand became widely used in quantum electronics. Lasersand laser facilities won sound position in all branches ofscience and industry. At that time YAG was consideredto be the best material for solid state high-e�cient CW,Q-switched and mode-locked lasers with low generationthreshold [1].

2. Application of the Czochralski methodfor the growth of laser crystals

During a short period of time, specialists from the In-stitute developed YAG laser element technology produc-tion according to OQG speci�cations. The technology ofYAG crystal production was introduced at an industrialplant.While working out the growth technology there was

chosen the optimal protective and reducing medium con-taining 98 vol.% of Ar + 2 vol.% of O2 which providedthe obtaining of crystals with high optical quality andwithout oxidation and failure of iridium crucibles. Thedeveloped design of crystallization unit provided the re-quired distribution of thermal �elds in the crystallizationzone and the axial temperature gradient. The opticalquality of the crystals was raised due to stabilization ofthe growth conditions achieved by means of automatedcontrol of the growth process. This allowed to decreasethe diameter of bulk defect in central region of crystalto ≈ 1 mm. Homogeneous YAG:Nd and YAG:Nd:Cr,Cegarnet crystals were obtained at a convex crystal�melt

(305)

306 M.B. Kosmyna et al.

interface. Variations of temperature of the crucible walldue to uncontrolled �uctuations of the power supplied tothe inductor and of melt temperature near the crystal�melt interface (at a depth less than 5 mm) did not exceed0.5�1 ◦C [1]. The obtained crystals had a length of 150�200 mm and a diameter of ≈ 35 mm (Fig. 1).

Fig. 1. Y3Al5O12:Nd3+ crystal and laser rod.

Due to unique capabilities of the Czochralski methodgrowth technologies of a number of compounds weredeveloped. In particular, the growth technology offorsterite (Mg2SiO4) single crystals was developed during1989�1993. The tunable lasers based on forsterite crys-tals were designed for the �rst time. The tunable range oflaser was 1170�1330 nm. The lasers were able to generateextra-short 25�30 fs pulses at 250 mW output power anddemonstrated a stable KLM regime operation under thesynchronous pumping.A series of nonlinear optic crystals was grown at the

Institute by means of the Czochralski method: lithiumniobate (LiNbO3), lithium tantalate (LiTaO3), fresnoite(Ba2TiSi2O8), KTiOPO4, and a number of borates(LiB3O5, Li2B4O7, β-BaB2O4) [2�4]. The method ofgrowth of lithium niobate and lithium tantalate crystalsdeveloped during 1983�1985 was brought into commer-cial production. For the �rst time, photorefractive resis-tant lithium tantalate crystals were obtained. The valueof resistance exceeded the one of the world analogues byan order of magnitude.The top seed solution growth method (TSSG) was

used at the Institute for the obtaining of nonlinearoptic and laser crystals. The production technolo-gies of neodymium and chromium doped Gd3Sc2Ga3O12

gadolinium scandium gallium garnets as well asneodymium doped KGd(WO4)2 potassium gadoliniumtungstate, were developed at the Institute during 1985�1989. Active laser elements based on the crystals pro-vide low threshold and high generation e�ciency at lowpumping energies. It allows to essentially decrease thedimensions, weight, and power consumption of laser facil-ities. The nonlinear optic borate single crystals (LiB3O5,β-BaBO4) were grown by the use of TSSG method, too.

The Institute has elaborated speci�cations for newequipment for growth of high-temperature oxide sin-gle crystals. High-frequency crystal growth units weredesigned for single crystal growth by the Czochralskimethod in collaboration with: �VNIITVCH� (Saint�Petersburg, Russia) � generation of setups �Kristall 603,605, 607�; TsKBM �Donets� (Lugansk, Ukraine) � setup�Landysh�; �TEKHMONTAG� (Lugansk, Ukraine) �setup �Analog�.The growth of single crystals from melt by the

Czochralski method has a number of advantages, such asthe absence of contact between the crystal and the cru-cible walls, that essentially reduces stresses in the crys-tals; the possibility to control the crystal growth visu-ally and the processes which occur at the crystal�meltinterface, relative simplicity of its technical realization.Moreover, the method allows to grow large-size and suf-�ciently perfect high-melting oxide crystals, to controlthe character of the melt convection and as consequence� to choose the most optimal conditions for the growthof optically homogeneous crystals. Possibilities of themethod are able to provide the obtaining of crystals ofdi�erent shape. The morphology of crystals is illustratedby Fig. 2.

Fig. 2. The crystals grown at di�erent vertical gradi-ents: a � LiNbO4; b � LiTaO4; c � PbWO4.

At low vertical gradients (∂T/∂z less than 10 deg/cm)the grown lithium niobate crystals are strongly faceted(Fig. 2a), at gradients of 30 deg/cm and higher thelithium niobate and lithium tantalate crystals are ofcylindrical shape (Fig. 2a, b).The shape of large-size PbWO4 single crystals (∅ ≥

50 cm) grown along the z axis was also di�erent fromcylindrical (Fig. 2c). The crystals of the preset di-ameter and rigorously cylindrical shape of the sur-face were obtained under the conditions when the ra-tio dcrystal/Dcrucible ≤ 0.45 held true during the wholegrowth process, and the axial gradients were ∂T/∂z ≈

Development of Growth Technologies for the Photonic Single Crystals . . . 307

25 deg/cm. In the case when 0.45 < dcrystal/Dcrucible <0.65 the crystal shape was at �rst cylindrical, but thenit was transformed into spiral (Fig. 2c).At the growth of PbWO4 crystals with a 50 mm diam-

eter, the level of the melt decreases faster than it takesplace during the growth of the crystal of a smaller diam-eter from the same crucible. Thereat, the crystal�meltinterface descends, and the magnitude of axial gradientis decreased, too. Thus, the magnitude of axial gradi-ent may be comparable with that of the radial gradients.A heat �ow along the growth axis may essentially de-crease with the rise of the growing crystal volume. TheIR radiation absorption by the growing crystal can a�ecton a heat �ow. The change of temperature distributionat crystal�melt interface as well as the crystal anisotropyof thermal conductivity may lead to the situation whenthe direction of the maximum heat transfer does not coin-cide with the growth direction. Such thermal conditionsresult in the formation of strong internal stresses andmake the morphology of PbWO4 crystal di�erent fromcylindrical one [5].The Institute was the �rst to realize the growth of YAG

crystals by the Czochralski method from �cold crucible�(crucible free, combination of the Czochralski methodand skull melting method) that provided the possibilityof saving expensive and scarce iridium used at crucibleproduction.A weighing of either the crucible containing the melt

or the growing crystal is generally used during the au-tomated process of crystal growth by the Czochralskimethod [6]. The choice of the weighing object depends onthe dimensions and total mass of the used crystallizationunit. The method of weighing the melt is considered tohave certain advantages when the total mass of the crys-tallization unit is up to 16 kg. At present the sensitivityis 0.01 g at a crystallization unit mass up to 10 kg.

Fig. 3. Automated �Analog� apparatus under controlof OS Windows.

Due to upgrading of the growth �Kristall-3M� setup acompletely automated �Analog� apparatus (Fig. 3) wasdesigned for growth of high-temperature oxide crystalsby the Czochralski method. The setup allows to growa wide range of crystals, including incongruent meltingcrystals or phase transition containing crystals (crystalgrowth from solution-melt).

3. PbWO4:Nd3+ and PbMoO4:Nd

3+ crystals forRaman lasers

For the major part of solid (non-diode) state lasers thelaser generation is realized by means of f−f emissionof rare-earth ions according to di�erent mechanisms ofenergy transformation (sensibilization, cross-relaxation,cascade generation, co-operative excitation) [7]. Sincethe crystal �eld weakly a�ects on the f state energy posi-tion, the luminescence maxima of rare earth ions slightlydepend on the crystal �eld of host. For the laser mediadoped with rare earth (RE3+) ions only one wavelength isdominant. The spectral range of such lasers is extendedby means of nonlinear optical e�ects. One of them is thetransformation of the emission wavelength due to the Ra-man scattering [8].A commercial Raman laser consists of an active laser

medium based on Al2O3:Ti or Y3Al5O12:Nd crystals andRaman converter, for example Ba(NO3)2 crystal. Tominimize the losses and to make the design of laser ap-paratus simpler and cheaper, the crystal must simultane-ously perform the functions of both active laser mediumand Raman converter. For this purpose PbWO4 leadtungstate and PbMoO4 lead molybdate are the mostpromising crystals [9]. Due to congruent melting ofPbWO4 (1141 ◦C) and PbMoO4 (1060 ◦C), it is possibleto successfully use the Czochralski method and to carryout the growth from platinum crucibles.One of the problems arising at the growth of tungstates

and molybdates of alkali earth element crystals is non--stoichiometric evaporation of melt, in particular, oftungsten and molybdenum oxides. This gives rise tochanges in the melt composition, the formation of var-ious point defects and their aggregation in the crystals.It leads to an essential variation of the physico-chemicalproperties along the crystal length. To reduce the in-�uence of these negative factors, an excess of tungsten(molybdenum) oxide (of about 1�3 mass%) is introducedinto the initial charge before crystal growth. Moreover,certain e�orts are taken to reduce an overheating of melt.To prevent an overheating of melt, di�erent crystalliza-tion units containing passive and active afterheaters, gascomposition, and pressure in the growth chamber areused.Another problem is the obtaining of crystals to be

used as active elements of lasers with diode pumping.In this case, in contrast to lasers with �ash-lamp pump-ing, the elements containing laser-active ions (e.g. Nd3+)which absorb 70�90% of the pumping energy at sev-eral millimetre length are required. Due to considerable

308 M.B. Kosmyna et al.

ionic radius mismatch, the growth of heavily neodymiumdoped alkali-earth tungstate and molybdate single crys-tals with optical and structural homogeneity is a sophis-ticated problem.Experimental choice of the growth conditions allowed

to successfully apply the Czochralski method for the crys-tal growth and production of active elements for theRaman lasers. We obtained Nd3+ doped PbWO4 andPbMoO4 crystals with a diameter of 25�30 mm anda length up to 200 mm. The Nd3+ concentration inPbWO4 and PbMoO4 crystals was up to 2 mass% andup to 3 mass%, respectively (Fig. 4) [10, 11].

Fig. 4. PbMoO4 single crystals and laser rod.

Experimental investigations of laser oscillations inPbWO4:Nd3+ and PbMoO4:Nd3+ crystals under di�er-ent pumping sources were carried out. Figure 5 presentsthe dependence of laser output energy on pumping en-ergy of diode laser for neodymium doped PbWO4:Nd3+

lead tungstate and PbMoO4:Nd3+ lead molybdate singlecrystals.

Fig. 5. Dependence of the output energy on thediode laser pumping energy for PbWO4:Nd

3+ andPbMoO4:Nd

3+ crystals.

Under diode laser pumping the 0.47 mJ generationthreshold and the 13.4% slope e�ciency were achievedfor PbWO4:Nd3+ crystal based laser. The 21% slopee�ciency obtained for PbMoO4:Nd3+ was the highest

among the crystals with the scheelite-type structure(Fig. 5) [12].The analysis of oscillation properties of tungstate and

molybdate crystals with the structure of scheelite-typeunder alexandrite and diode laser pumping testi�es thatthe highest slope e�ciency is achieved for PbWO4:Nd3+

and PbMoO4:Nd3+ crystals. The crystals with suchstructure type are characterized by higher peak Ramancross-sections, lower SRS thresholds, higher Raman gain,and greater Raman conversion e�ciency in comparisonwith those of commercial KGd(WO4)2:Nd crystal.For the PbWO4:Nd3+ and PbMoO4:Nd3+ based lasers

in the passively Q-switched mode laser generation wasrealized simultaneously with SRS conversion [12, 13]. ForPbMoO4:Nd3+ laser self Raman operation at 1163 nm(1st Stokes) was achieved for the �rst time [13].A new compound was revealed while studying the

quasi-binary system PbMoO4+Nd2(MoO4)3. For the�rst time, a series of experiments resulted in the obtain-ing of PbNd4(MoO4)7 single crystals by the Czochralskimethod from the melt of the stoichiometric composition.The crystals with a diameter up to 20 mm and a lengthup to 40 mm were grown from platinum crucibles in air(Fig. 6) [14].

Fig. 6. PbNd4(MoO4)7 single crystals.

The structure interpretation of PbNd4(MoO4)7 singlecrystal showed that the compound belongs to monoclinicsystem, the space group C2/c. The unit cell parame-ters are: a = 16.8585 Å, b = 11.8022 Å, c = 11.8529 Å,β = 98.080◦. Cations of lead and neodymium are co-ordinated by eight oxygen atoms, whereas molybdenumcations are linked with four oxygen atoms. Neodymiumcations occupy two crystallographic positions. The unitcell of PbNd4(MoO4)7 crystal is presented in Fig. 7.Due to spatial separation of neodymium cations in the

crystal lattice, concentration quenching of f�f lumines-cence of Nd3+ ions is reduced. Investigation of Nd3+

luminescence decay kinetics shows that the luminescencedecay curve is approximated by the sum of two compo-nents with the times τ1 = 1.1 µs and τ2 = 3.5 µs. Thepresence of two decay times points to the existence oftwo luminescence centres with non-equivalent Nd3+ sur-rounding and con�rms the data of X-ray structure anal-

Development of Growth Technologies for the Photonic Single Crystals . . . 309

Fig. 7. Unit cell of PbNd4(MoO4)7 crystal.

ysis which shows that Nd3+ cations can occupy not onlytheir own crystallographic position, but also the one oflead [14]. Thus, the new PbNd4(MoO4)7 crystal may addto the series of self-concentrated crystal hosts for activelaser media.

4. Scintillation single crystals

4.1. PbWO4 crystals

The Czochralski method was considered to be the mostsuitable for large-scale industrial production of PbWO4

crystals. In particular, it was used to provide hugeamounts of these crystals (about 100 000 scintillation el-ements) for the CMC and ALICE projects at CERN [15].A crystal growth technology of large-size PbWO4 crys-

tals (35 mm in diameter and 250 mm long) for scin-tillation detectors was developed at Institute. It ischaracterized by comprehensive approach to technolog-ical preparation of the starting material (including re--crystallization) and to the doping of the crystals withdi�erent ions for the formation of preset properties, suchas maximum position of luminescence spectrum, radia-tion hardness, absence of colour centres which re-absorbthe host luminescence [15].Experimental investigations of PbWO4 crystal growth

were carried out by use of the setups with high-frequencyheating �Crystal 3M� and �Analog�. Lead tungstate crys-tals were grown by the Czochralski method from plat-inum crucibles in an atmosphere with a composition closeto that of air or inert gases. At �rst the homogeneousmechanical mixture of tungsten and lead oxides (99.999%purity) was melted to increase the density and performpreliminary synthesis.For additional puri�cation, averaging of the chemi-

cal composition, as well as for reducing the deviationfrom the stoichiometry, the charge was preliminarily re--crystallized. During successive crystallization processesthe melt composition is being corrected, the doping isrealized taking into account the measurements of the pa-rameters of the scintillation elements. Lanthanum, yt-trium or niobium doped PbWO4 crystals were grown.The dopant concentration was few tens of ppm. The

single crystals and rectangular scintillation elements areshown in Fig. 8.

Fig. 8. PbWO4 single crystal and scintillationelements.

The Czochralski method was successively applied forcrystal growth where the formation of preset propertieswas achieved by modi�cation of both the cationic andanionic sublattices. Experimental choice of growth con-ditions and dopants for modi�cation of the cationic andanionic sublattices of PbWO4 crystal allows to controlthe properties of these crystals within wide range, in par-ticular, to vary the luminescence kinetics and position ofhost luminescence maximum and to achieve essential in-crease of light yield or radiation hardness, for example[16�18].

4.2. CdWO4 crystals

At present time, multi-energy radiation control sys-tems containing multi-element scintillation detectorsbased on cadmium tungstate crystals are actively devel-oped. The new generation of devices formulates stringentrequirements for scintillation assemblies based on cad-mium tungstate crystals. Each detector array meant forintroscopic systems requires several thousands elementswith high identity of scintillation parameters.The growth technology of CdWO4 crystals for scintil-

lation detection unit and elements of detector arrays withpreset dimensions was developed at the Institute.As mentioned earlier, the main problem arising at the

growth of these crystals is evaporation of the melt whichleads to ≈ 2−3% losses of the melt weight. We carriedout investigations aimed at minimization of the melt sur-face area due to the growth of crystals with largest pos-sible diameter from a crucible of relatively small size.The growth of large CdWO4 crystals with a diameterapproaching the crucible diameter (100 mm) makes itpossible to decrease evaporation of the melt at high tem-peratures, since in this case the melt surface area notcovered by the growing crystal, is minimized.Certain corrections were introduced into the growth

technology, in particular, in the composition of chargeand the temperature distribution inside the crystalliza-tion unit. That allowed to reproducibly obtain high--quality colourless CdWO4 crystals with a diameter up

310 M.B. Kosmyna et al.

Fig. 9. CdWO4 single crystals.

to 65 mm and a length up to 160 mm from the melt of≈ 800 cm3 volume (Fig. 9) [19]. The growth of crys-tals with high optical homogeneity and strictly speci�eddimensions made possible the reproduction of scintilla-tion elements for detector arrays at minimum losses ofmaterial.The large-volume (≈ 350 cm3) scintillation detection

unit with high (≈ 16%) energy resolution (137Cs, E =662 keV) was designed in the Institute for the �rst timedue to developed growth technology of optically homoge-neous and perfect CdWO4 crystals. The detection unitcan be applied high-e�cient gamma-spectrometric por-tals that can detect neutrons, too.

5. Growth of new CdRE2(WO4)4(RE = La, Gd) single crystals

With the purpose of widening the scintillation crystalfamily, the search for new compounds was done. Accord-ing to the crystal chemistry approach, new phases canbe obtained by transformation of known phase by meansof change of its composition. Double tungstates may beconsidered as a result of modi�cation of the cationic oranionic sublattices. Thereat, the phases of substitution,subtraction and incorporation can be formed.Due to congruent melting and the absence of poly-

morphic transformations of the synthesized stoichiomet-ric compounds CdLa2(WO4)4 and CdGd2(WO4)4 theCzochralski method was used for single crystal growth.The growth process of CdLa2(WO4)4 and CdGd2(WO4)4crystals can be carried out in air from platinum cruciblesbecause of melting temperatures 1090 ◦C and 1166 ◦C,respectively. The crystallization unit specially devel-oped for the obtaining of CdWO4 crystals was used togrow CdLa2(WO4)4 and CdGd2(WO4)4 single crystals.This unit contains the system of active and passive after-heaters which provide the optimum distribution of tem-perature in the zone of growth and subsequent annealingof the obtained crystal. The design of such unit per-mits to essentially reduce evaporation of melt and growa boule with a volume up to 70% of melt volume.The authors carried out a series of experimental growth

of the crystals at varying temperature conditions. As a

result, CdLa2(WO4)4 and CdGd2(WO4)4 crystals weregrown for the �rst time. The diameter was up to 20 mmand a length � up to 40 mm (Fig. 10).

Fig. 10. Fragments of CdLa2(WO4)4 andCdGd2(WO4)4 single crystals: a �CdLa2(WO4)4:Nd

3+, b � CdGd2(WO4)4, c �CdGd2(WO4)4:Nd

3+.

The study of their scintillation characteristics showedthat the light yield of CdGd2(WO4)4 is extremely low.It is less than 1% that of CdWO4 crystal. Though thelight yield of CdLa2(WO4)4 crystal is on the level of23% CdWO4 light yield, their luminescence characteris-tics turn out to be instable with time. In several monthsthe light yield of CdLa2(WO4)4 dropped dramaticallyand was also less than 1%.Nevertheless, we showed the possibility of

CdLa2(WO4)4 and CdGd2(WO4)4 crystal growth. Fur-ther improvement of CdLa2(WO4)4 and CdGd2(WO4)4crystal growth technology and the presence of 116Cdand 180W isotopes in their composition may providesuccessful use of the crystals in studies of rare nuclearreactions, such as the 2β decay [20].To test the lasing properties of disordered

CdRE2(WO4)4 (RE = La, Gd) double tungstateswe grew the Nd3+-doped crystals (Fig. 10a, c).Some characteristics of CdLa2(WO4)4:Nd3+ andCdGd2(WO4)4:Nd3+ are presented in Table.

TABLE

Spectral, kinetic and lasing characteristics ofCdLa2(WO4)4:Nd

3+ and CdGd2(WO4)4:Nd3+ crystals.

CNd

[mass%]

τ [µs]

(λ = 1064 nm)

Opticalbreakdown[J/cm2]

Slopee�ciencyηsl [%]

CdLa2(WO4)4 0.9 130 61 �

CdGd2(WO4)4 1 90 52 1.3

Development of Growth Technologies for the Photonic Single Crystals . . . 311

Laser oscillations in free-running mode under laserdiode pumping for CdGd2(WO4)4:Nd3+ crystals were ob-tained. The slope e�ciency was 1.3%. Laser oscillationswere not observed for CdLa2(WO4)4:Nd3+ crystal.

6. Double vanadate single crystals:growth and properties

An interest in double vanadate crystals ofCa9RE(VO4)7 type is caused by the use of suchcrystal hosts for laser engineering and nonlinear optics.The crystals belong to the noncentrosymmetric spacegroup R3c, therefore they can be applied for the secondharmonic generation (SHG). A quantitative estimationof SHG e�ciency for polycrystalline Ca9RE(VO4)7 sam-ples (with 3�5 µm grain dispersion) was made in [21].The SHG e�ciency in the crystals of Ca9RE(VO4)7family was shown to be by 20�40 times higher incomparison with that of quartz.The compounds Ca9RE(VO4)7 (RE = Y, La, Gd) are

congruently melted at Tmelt ≈ 1500 ◦C. Moreover, thesecrystals are characterized by the polymorphic transitionfrom the noncentrosymmetric to the centrosymmetricphase [21]. The phase transition temperatures lie within800�1100 ◦C range.The crystals with high optical nonlinearity are consid-

ered as promising active laser media. The use of diodepumping imposes certain requirements to active laser el-ements. In this aspect, double vanadate crystals have anumber of advantages.Disordering of Ca9RE(VO4)7 crystal structure must

result in the widening of dopant spectral bands. Thereat,the wavelength temperature stability of diode laser atpumping of the crystals containing ions with narrow ab-sorption bands, like Nd3+, is not so critical.At Yb3+ doping such crystal host may show ampli�-

cation in a wide spectral band and produce ultra-shortlaser pulses [22]. Moreover, high level of laser-active ionsdoping can be achieved for such hosts. This will allow toprovide high coe�cient of pumping energy absorption ata small laser element depth and, consequently, to minia-turize the laser apparatus.Due to peculiarities of the structure of Ca9RE(VO4)7

vanadates, we can select pairs of rare-earth cations(cation of host + activator cation) and control their dis-tribution to the crystallographic positions, thus creatingdi�erent activator centres. The spatially separated poly-hedrons in the crystal structure of vanadates containingrare-earth cation will reduce the exchange interaction be-tween the activator ions and increase their concentrationin the crystal without luminescence quenching [23].Owing to the presence of vacant positions in the crystal

structure, these vanadates are distinguished by high ionicconductivity and di�usion caused by migration of the ionsinto the cationic sublattices [24].A number of papers devoted to the growth of

Ca9RE(VO4)7 (RE = Y, La, Gd) crystals and investi-gation of their spectroscopic properties at Nd3+-doping

were published during the past ten years [25�27]. The au-thors of [25�27] have grown the crystals by direct pullingfrom the melt using the Czochralski method. However,strong scattering of laser beam passing through the crys-tal bulk is an essential problem limiting the use of suchcrystals for nonlinear optics and lasers. The causes ofthe scattering, though being actively discussed, have notbeen elucidated so far.The growth of double vanadate Ca9RE(VO4)7 (RE =

Y, La, Gd) single crystals and the study of their prop-erties were also carried out at the Institute. Taking intoaccount their high melting temperature (≈ 1500 ◦C), thecrystals were grown in argon or nitrogen atmosphere inIr crucibles (∅ = 60 mm, h = 70 mm) by means of�Kristall 3M� and �Analog� setups with inductive heat-ing and an automated control diameter system of grow-ing crystal. The crystal growth was carried out along thecrystallographic axis [001].Under the described conditions nominally pure and

doped Ca9RE(VO4)7 (RE = Y, La, Gd) single crystalswere grown. The growth process is reported in detailin [28]. According to the data of chemical analysis, the to-tal concentration of uncontrolled impurities in each crys-tal was not higher than (2�3)×10−3 mass%. The crystalshad a diameter up to 25 mm and a length up to 80 mm.The scattering centres in crystals were studied by

means of optical and electron microscopy. According tothe obtained data, the crystals did not contain micron-and submicron-size gaseous phase inclusions. Neitherinclusions of the crucible material (iridium) nor microcracks were observed. At the same time, the energy dis-persive X-ray analysis of crystals showed inhomogeneityof composition. Within the crystal, inclusions of severalmicrometer sizes with a distinct compositional contrastwere observed. According to the element analysis, theseinclusions were enriched with a rare-earth element. Themaximum density of the enriched regions was observedfor Ca9Gd(VO4)7 crystal [28].On the basis of crystals structure peculiarities of

Ca9RE(VO4)7 compounds and aiming at the obtaining ofsingle crystals with homogeneous composition, we madean attempt to grow Ca10Me(VO4)7 (Me = Li, Na, K) sin-gle crystals. The crystal lattice of Ca10Me(VO4)7 (Me =Li, Na, K) compounds does not contain vacant crystal-lographic positions. The regimes and conditions werethe same as for Ca9RE(VO4)7 crystal growth. Thus,the Ca10 M(VO4)7 (M = Li, Na, K) single crystals weregrown for the �rst time. Fragments of crystals are shownin Fig. 11.On the base of obtained data on scattering centers,

real compositions of obtained double vanadate crystalsand growth conditions, the compositions of crystals wereexperimentally selected, and a number of Nd3+, Yb3+

and Er3+-doped single crystals were grown.Preliminary experimental study of laser oscilla-

tion allowed to obtain 0.87% slope e�ciency forCa10Li(VO4)7:Nd3+ crystal at �ash-lamp pumping infree-running mode (Fig. 12). Thereat, the Nd3+ con-

312 M.B. Kosmyna et al.

Fig. 11. Fragments of double vanadate crystals: a �Ca10Li(VO4)7, b � Ca10Na(VO4)7, c � Ca10K(VO4)7.

Fig. 12. Laser output of Ca10Li(VO4)7:Nd3+ crystals

vs. the electrical �ash-lamp energy. Inset � laser out-put of Y3Al5O12:Nd

3+ and Y2O3:Nd3+ crystals from

Ref. [29].

centration and the laser generation conditions were notoptimal. Nevertheless, the obtained e�ciency value isclose to that of commercial Y3Al5O12:Nd3+ crystal andexceeds the e�ciency of Y2O3:Nd3+ at �ash-lamp pump-ing in free-running mode (the inset in Fig. 12) [29].Thus, taking into account physico-chemical investiga-

tions, we obtained new single crystal hosts for nonlinearoptics and laser engineering by means of the Czochralskimethod [30].

7. Conclusions

Using the Czochralski method during the whole periodof the existence of Institute for Single Crystals, NAS ofUkraine the specialists from the Institute obtained a largenumber of laser, nonlinear optical and scintillation crys-

tals and developed industrial highly e�cient technologiesof crystal growth.Five generations of crystal growth setups were designed

according to speci�cations of the Institute. The methodwas used for the growth of approximately 30 types of one-and multi-component single crystals.The Czochralski method permits easily change of the

thermal �elds and crystal growth conditions, to controlthe dimensions and shape of the growing crystals. Thismakes the method unique and suitable for the obtain-ing of crystals, such as Si, Ge, Y3Al5O12:Nd, Al2O3:Ti,CdWO4, PbWO4, Bi3Ge5O12, etc. for both, scienti�c re-search and a number of commercial applications.The Czochralski method is universal and widely used.

At present it is successfully applied for the obtaining ofa wide range of crystals with di�erent composition andmelting temperature, that makes a valuable contributionto the development of Hi-Tech industry.

References

[1] Handbook of Lasers, Ed. F. Trager, Springer-Verlag,Berlin 2012.

[2] M.B. Kosmyna, A.P. Voronov, S.F. Prokopovich,O.P. Balva, USSR Patent #807688, 20.07.1979.

[3] M.B. Kosmyna, A.B. Levin, A.I. Mashkov, N.F. Efre-mova, Russian Federation Patent #1468025,21.07.1987.

[4] V.A. Aslanov, M.B. Kosmyna, A.A. Frolov,O.B. Struver, Russian Federation Patent #1568593,28.06.1988.

[5] Yu.N. Gorobets, M.B. Kosmyna, B.P. Nazarenko,A.N. Shekhovtsov, Funct. Mater. 13, 400 (2006).

[6] D. Mateika, in: Current Topics in Materials Science,Vol. 11, Ed. E. Kaldis, North-Holland, Amsterdam1984, p. 153.

[7] Handbook of Lasers, Ed. M.J. Weber, CRC PressLLC, Boca Raton 2001.

[8] R.C. Powell, T.T. Basiev, in: Handbook of LaserTechnology and Applications, Eds. J.D.C. Jones,C.E. Webb, Taylor&Francis Group, CRC Press, BocaRaton 2003, p. 467.

[9] T.T. Basiev, Phys. Usp. 42, 1051 (1999).

[10] V.N. Baumer, Yu.T. Dynnik, M.B. Kosmyna,B.P. Nazarenko, V.M. Puzikov, A.N. Shekhovtsov,V.F. Tkachenko, Opt. Mater. 30, 106 (2006).

[11] Yu.N. Gorobets, M.B. Kosmyna, A.P. Luchechko,B.P. Nazarenko, V.M. Puzikov, A.N. Shekhovtsov,D.Yu. Sugak, J. Cryst. Growth 318, 687 (2011).

[12] T.T. Basiev, M.E. Doroshenko, L.I. Ivleva,V.V. Osiko, M.B. Kosmyna, V.K. Komar, J. Sulc,H. Jelinkova, Quant. Electron. 36, 720 (2006).

[13] T.T. Basiev, S.V. Vassiliev, M.E. Doroshenko,V.V. Osiko, V.M. Puzikov, M.B. Kosmyna, Opt.Lett. 31, 65 (2006).

[14] T.T. Basiev, V.N. Baumer, Yu.N. Gorobets,M.E. Doroshenko, M.B. Kosmyna, B.P. Nazarenko,V.V. Osiko, V.M. Puzikov, A.N. Shekhovtsov, Cryst.Rep. 54, 697 (2009).

Development of Growth Technologies for the Photonic Single Crystals . . . 313

[15] P. Lecoq, A. Annenkov, A. Gektin, M. Korzhik,C. Pedrini, Inorganic Scintillator for Detector Sys-tems, Springer-Verlag, Berlin 2006.

[16] B.V. Grinyov, M.B. Kosmyna, V.R. Lyubinskiy,B.P. Nazarenko, P.V. Nomokonov, V.M. Puzikov,A.S. Vodopianov, Funct. Mater. 8, 729 (2001).

[17] V.N. Baumer, Yu.N. Gorobets, O.V. Zelenskaya,M.B. Kosmyna, B.P. Nazarenko, V.M. Puzikov,A.N. Shekhovtsov, Cryst. Rep. 53, 1252 (2008).

[18] N.R. Krutyak, V.V. Mikhailin, D.A. Spassky,V.N. Kolobanov, M.B. Kosmyna, B.P. Nazarenko,V.M. Puzikov, A.N. Shekhovtsov, J. Appl. Spectr.79, 228 (2012).

[19] M.B. Kosmyna, B.P. Nazarenko, V.M. Puzikov,A.N. Shekhovtsov, A.A. Ananenko, Yu.A. Borodenko,B.V. Grinyov, Yu.S. Koz'min, V.A. Tarasov, Cryst.Rep. 54, 165 (2009).

[20] L. Bardelli, M. Bini, P.G. Bizzeti, L. Carraresi,F.A. Danevich, T.F. Fazzini, B.V. Grinyov,N.V. Ivannikova, V.V. Kobychev, B.N. Kropivyansky,P.R. Maurenzig, L.L. Nagornaya, S.S. Nagorny,A.S. Nikolaiko, A.A. Pavlyuk, I.M. Solsky,M.V. Sopinskyy, Yu.G. Stenin, F. Taccetti,V.I. Tretyak, Ya.V. Vasiliev, S.S. Yurchenko,Nucl. Instrum. Methods Phys. Res. A 569, 743(2006).

[21] B.I. Lazoryak, A.A. Belik, S.Yu. Stefanovich,V.A. Morozov, A.P. Malakho, O.V. Baryshnikova,I.A. Leonidov, O.N. Leonidova, Dokl. Phys. Chem.384, 144 (2002).

[22] P.H. Haumesser, R. Gaumé, B. Viana, D. Vivien,J. Opt. Soc. Am. B 19, 2365 (2002).

[23] B.I. Lazoryak, Russ. Chem. Rev. 65, 287 (1996).

[24] I.A. Leonidov, M.Ya. Khodos, A.A. Fotiev,A.S. Zhukovskaya, Inorg. Mater. 24, 347 (1988) (inRussian).

[25] Z.B. Lin, G.F. Wang, L.H. Zhang, J. Cryst. Growth304, 233 (2007).

[26] X. Hu, X. Chen, N. Zhuang, R. Wang, J. Chen,J. Cryst. Growth 310, 5423 (2008).

[27] L. Li, G. Wang, Y. Huang, L. Zhang, Z. Lin, G. Wang,J. Cryst. Growth 314, 331 (2011).

[28] M.V. Dobrotvorskaya, Yu.N. Gorobets, M.B. Kos-myna, P.V. Mateichenko, B.P. Nazarenko,V.M. Puzikov, A.N. Shekhovtsov, Cryst. Rep.57, 86 (2012).

[29] B.M. Walsh, J.M. McMahon, W.C. Edwards,N.P. Barnes, R.W. Equall, R.L. Hutcheson, J. Opt.Soc. Am. B 19, 2893 (2002).

[30] Yu.A. Zagoruiko, V.K. Komar, M.B. Kosmyna,N.O. Kovalenko, B.P. Nazarenko, A.N. Shekhovtsov,in: Crystal Materials for Optics and Electronics, Ed.V.M. Puzikov, ISC Press, Kharkov 2012, p. 476 (inRussian).